Is the evidence for fish-eating better than simply taking a fish oil pill?
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The omega-3 industry is in a twist. Again. Last week, Cochrane, an organisation that compiles and evaluates medical research for the general public, released a meta-analysis – a study of studies – to determine whether or not omega-3 pills, one of the world’s most popular dietary supplements, reduced the risk of coronary heart disease. After comparing 79 trials involving 112,059 people, the researchers could find “little or no difference to risk of cardiovascular events, coronary heart deaths, coronary heart disease events, stroke or heart irregularities”.

I can’t say that I was particularly surprised. Over the past 15 years, more than 20 studies have shown a similar lack of effect. But what does surprise me is how we continue to look at the world of fish and seafood through the amber lens of a fish oil capsule. Omega-3s do something in our bodies – and probably something important. But without the larger context of the marine organisms that contain them, omega-3s get lost in the noise of human metabolism and modern marketing.

The confusion arises in part from the historical baggage of fish oil and the $30bn (£23bn) industry associated with omega-3 extraction. Once upon a time, fish oil solved a major human health problem. But it had nothing to do with coronary heart disease. During the Industrial Revolution, a disease became increasingly prevalent throughout northern Europe: rickets. Malnourished children in sunlight-poor urban slums often ended up bowlegged by adolescence. Researchers eventually pieced the puzzle together and concluded that the disease was caused by a deficiency in vitamin D, which the body naturally generates in the presence of sunlight. And, as it turned out, vitamin D is stored in high amounts within the liver of codfish.

A Norwegian pharmacist named Peter Möller seized upon this finding (and many other anecdotal stories about the curative properties of cod-liver oil). Using a patented chemical process, he arrived at a product that, he announced to the world, “didn’t taste fishy”. Möller and his advertising team then launched a campaign to institutionalise the regular use of cod-liver oil, regardless of whether you were at risk of rickets or not. The campaign was a success: a spoonful a day became common practice. Möller built his company into an international presence and died in 1869 with 70 cod-liver oil steam factories to his name, churning out 5,000 barrels of the stuff a year. By the time omega-3s started to be a focus of medical research, there was already a rosy feeling around fish oil.

In the early 1970s, the chemist Hans Olaf Bang read in a Danish journal that there were extremely low incidences of cardiovascular disease in Inuit communities of Greenland. He and his assistant, Jørn Dyerberg, travelled to Uummannaq on the north-west coast of Greenland to investigate. At the time of the expedition, Bang didn’t quite know what he wanted to test for. They probed and palpated 130 local people, measured height and weight, and came home with a lot of blood.

“We had these 130 precious samples of blood,” Dyerberg told me in his lab in Copenhagen recently. They estimated that in 20 years, the traditional Inuit diet would have changed to the western diet, and Dyerberg remembers Bang saying: “‘There will never be anyone who can do this again, so let’s do whatever we can!’ And we decided to do fatty acid analysis.”

The result of their analysis was a hypothesis that is an exemplary “association study”. In an association study, multiple factors are logged and a hypothesis of correlation is drawn from the findings. In the case of the Bang and Dyerberg Inuit study, they found that: 1) Inuit people in Greenland had a diet high in omega-3 fatty acids and blood lipid levels of omega-3s much higher than their western contemporaries. 2) Inuit people also had, according to public health records, markedly lower rates of coronary heart disease. They hypothesised that therefore 3) omega-3s might reduce the risk of coronary heart disease.

This was backed up by further laboratory studies that did show, in vitro, that omega-3s were involved in anti-inflammatory reactions. But – and this is a big but – while correlations abound for omega-3s and heart disease, the real trouble has always been in showing causation. That is where this latest round of studies comes in.

The Cochrane study and the others that preceded it have one thing in common: they are meta-analyses of “randomised control trials” (RCTs). That is, trials where patients are given a supplement at random and tracked over time against another set of patients given a placebo. Most statisticians consider these trials to be the very top of the evidence pyramid. But it is these studies that have at times proven troublesome for Omega World. Each time RCTs come to light that show little or no effect, Omega World tends to blend its counterargument with evidence from association studies because, as a recent industry reply to the Cochrane report put it, “it’s all connected”.

When it then turns to the RCTs, the industry, as would be expected, looks for different explanations as to why positive health outcomes weren’t reported. In the burst of RCTs preceding Cochrane, the Omega World line was that these most recent trials did not show benefits because things such as statins, stents and other forms of cardiovascular intervention masked the anti-inflammatory effect of fish oil pills; earlier RCTs had shown a fairly significant effect, but none of those treatments existed at the time of those trials.

The industry also, and I believe rightly, pointed out that studies often failed to look at omega-3 blood lipid levels before and after supplementation. In other words, it’s not really a fair trial if you don’t know where the patients started with respect to the omega-3 levels in their blood. If we only measure effect without looking at omega-3 levels in the blood at the outset, aren’t we doing the dietary equivalent of testing how far a car can drive without checking how much petrol is in the tank at the start?

With Cochrane, the latest industry argument is that the study’s authors cut out a number of different forms of cardiac ailments, thus skewing the stats. In particular, it notes that Cochrane failed to include “sudden cardiac death” and “sudden cardiac mortality” in its list of outcomes. Since nearly half of all patients first report heart disease to their doctors by suddenly dropping dead, this is not an insignificant exclusion.

But the fact that the industry’s arguments shift with each new, damning meta-analysis gives you pause. What is going on? Is there an international conspiracy to discredit omega-3s? Or does Omega World keep moving the goalposts? When I posed this question to Ellen Schutt, the executive director of the Global Organization for EPA and DHA Omega-3s, probably the world’s most prominent omega-3 advocacy organisation, she made it seem as if the problem didn’t even exist. “As a matter of fact, we track media sentiment … and have found many more positive omega-3 stories than negative, in general. Of course, the negative stories are the ones that catch people’s attention. As we both know, negative stories are much more interesting and the media is definitely guilty of sensationalist ‘clickbait’ headlines such as: ‘Omega-3s don’t work.’”

As sympathetic as I am to the trials of Omega World, as studies continue to poke holes in aspects of the omega-3 cardiovascular argument, I can’t help thinking there is something else going on. Because, while the fish oil supplement business is a big deal, it is also a sheen on the surface of a much deeper pond. Long before omega-3 supplements became popular, an industry arose that used the same omega-3-rich creatures not for medicine, but for an odd array of agricultural and industrial purposes.

Ultimately, it was this so-called “reduction industry” that created the oily-fish extraction system that now consumes millions of tonnes of marine wildlife every year. Today, one in every four kilograms of fish caught is reduced into oil and meal and used for agriculture, land animal husbandry and, most recently, fish farming, AKA aquaculture.

The reduction industry has appeared in different forms under different ownership over centuries of human history. In the 18th century, it targeted whales, reducing northern hemisphere cetacean populations into isolated pockets of endangered species in order to make lamp oil and lubricants. In the 19th and early 20th centuries, it shifted to the southern hemisphere, reducing 390,000 of the 400,000 great whales that once roamed the Southern Ocean to margarine, nitroglycerine and other “marine ingredients”.

In the latter half of the 20th century, it shifted again and targeted small, oily fish such as anchovies, sardines and herring. In the late 1940s and early 1950s, the largest reduction operation in human history arose off the coast of Peru in pursuit of the Peruvian anchoveta. The Peruvian anchoveta is by far the largest single species catch by tonnage in the world, some years comprising as much as 10% of all fish caught. And although Peruvian anchoveta are as delicious as any anchovy on Earth, an industry-influenced Peruvian law dictates that more than 95% of the catch must go to the reduction industry.

Each decade brings a different use for all those anchovies. In the 1940s, they were used for fertiliser. In the 50s and 60s, chicken feed. In the 70s, pet food and pig feed. In the 80s and 90s, aquafeed for salmon and other carnivorous fish. And now, the most elite product of the reduction industry: dietary supplements.

And it is not just Peruvian anchoveta that are reduced into fish meal and oil. All told, the reduction industry removes from the ocean 20m-25m tonnes annually – the equivalent of the combined weight of the population of the United States. The omega-3 industry argues that some vendors are turning to much more sustainable options, such as algae-based omega-3s and fish oil reclaimed from recycled byproducts.

Nevertheless, the reduction industry marches on into new territory. Most recently, it has begun targeting Antarctic krill, the keystone prey species of the entire Antarctic ecosystem. Two years ago, when I asked the then chief executive of the largest krill extractor in the world why it had launched a $200m fishing operation in the Southern Ocean to take food out of the mouths of whales, he noted that krill oil is a “phospholipid” and making it much more “bioavailable” means that consumers can take a much smaller pill. Why was this important? Consumers who chose krill oil over fish oil would be much less likely to suffer the horrors of a fishy burp.

Amid all the conflicting reports, there is one bit of data that shines out: fish and seafood can bring considerable health and environmental benefits. Fish, in addition to providing us with omega-3s, delivers protein with far fewer calories than meat: 100g of salmon contains 139 calories and 23g of protein. By comparison, 100g of beef contains 210 calories and 20g of protein.

Harvesting wild fish from well-managed stocks requires a fraction of the carbon as farming terrestrial livestock. Similarly, fish farming puts a lesser burden on the Earth in terms of carbon and freshwater use than pretty much any form of terrestrial animal husbandry. We could make the farming of fish even more carbon- and resource-efficient if we used alternative ingredients for fish food based on algae and food waste. And if you consider growing “filter feeders” such as mussels, clams and oysters, the benefits are even more extreme. These bivalves don’t have to be fed anything, and make water cleaner even as they grow fatter. They provide protein 30 times more efficiently than cattle.

Is the epidemiological evidence for fish-eating better than simply taking a fish oil pill? Again, we are stuck with the problem of correlation versus causation. It is very difficult to feed someone a fish in such a manner that they don’t know they are eating a fish. Hence an RCT of seafood-eating hasn’t really ever been done. Most of the studies around seafood are association studies. And, while one such study associated eating fish twice a week with a possible reduction in mortality of 55,000 lives a year, we don’t know what a fish-eater does with the rest of their life beyond eating fish.

But what we do know is this: the omega-3 industry and the reduction industry that bred it removes fish from the water in a way that doesn’t put protein on our plates – it just puts pills in our cupboards. Is this the way we want to continue to do business with the planet?

• The subheading of this article was amended on 25 July 2018 to clarify that it was for heart health or strokes that the study found omega-3 had little or no benefit.

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